Radio television system



NOV. 3, 1931. E L NELSQN I 1,830,173

RADIO TELEVIS ION SYSTEM Filed June 25, 1927" 2 sheet's-sheet 1 v d u 'W j [d -41' B1? IlI RADIO SYN REC /N VEN TOR 50W/1 H0 L Naso/v Nov. 3, 1931: E. L. NELSON RADIO TELEVISION SYSTEM 2 Sheets-Sheet 2 n i nA mN A m4 M f Patented Nov. 3, 1931 UNITED STATES PATENT OFFICE EDWARD L. "NELSON, OF MOUNTAIN LAKES, NEW'JERSEY, ASSIGNOR- TO 'BELL TELE- PHGNE LLABORATCBES, IHCORPGRATED, E' NEVI YC'RK, N. Y., A CCRPORATION 0F NEW YORK RADIO TELEVISION' SYSTEM .application filed .Tune 23,

This invention relates to electro-optical transmission systems and particularly to radio television. l

The transmission to a remote point of an image of an object or scene` is based upon the analysis of the object point by point in a time sequence and thc transmission of waves having characteristics corresponding to the variations freni point to point of the light and r hade characteristics of the obj-ect. The transmitted waves are then utilized to control at a receiving point the formation of an image which is built up point-by point in the time sequence corresponding tothat of the analysis of the object.

ln order to produce a satisfactory image of a moving object it is necesary to transmit a band of waves of relatively great width- 20,000 cycles per second, for exampleand to reduce interference of all kinds to a low value. The elimination of interference and distortion when radio transmission is employed to transmit the image waves becomes a very difficult problem. Among the problems which had to be solved were the following:

he transmitting antenna should be tuned to permit effective radiation, but the side band ot the carrier is so wide that distortion in the outermost portions of the band is likely to occur. 'l` he receiving antenna should be tuned to eliminate interference but here again distortion must be guarded against. The photoelectric currents are very minute andthe power radiated must be large, so that very great amplification must be resorted to at the transmitter, out this large amount of power introduces disturbances in the circuits carrying minute currents which are large compared with these currents. Prior to this invention there was, so far as applicant is aware, no

hn receiving system capable of eliminating- .n..urbing wavs, which did not produce iirohihitive distortion. rllhe most nearlysuitable circuit arrangement from the point of view of selectivity and band width was the fio-called superheterodyne arrangement, but, due to the wilth of the frequency band, the usual type of radiofrequency input rcircuits employed with the superheterodyne could not be used.

1927. seria; No. 200,305.

ln accordance with this invention, a system is provided which avoids the above mentioned difiiculties. At the transmitting station the weak photoelectric currents are greatly amplified and used to modulate a carrier currentof such high frequency that the distortion of the side band frequencies in the antenna circuit becomesv negligible. This frequency may, for example, belOO kilocycles. At the receiver initial selectivity is obtained by coupling a. local circuit containing resistance to the antenna thereby securing a widened resonance characteristic. The carrier frequency is then combined with a current from a local source ofV frequency very much higher .fo that the resulting difference frequency7 is much higher than the received carrier. This reduces the percentage width of the de band to such an extent that selectivity maybe obtained in tuned circuits, without undue distortion and at the same time eliminates interference from the harmonics of the local source, which are of such high frequency as to be harmless. The frequency of the local source may be 6500 lrilocycles, for examplev` in which case the difference frequency 500() kilocycles. After passage through highly selective circuits this latter current is combined with current from another local source for producing an intermediate difference frequency, which, after being` selectively amplified, is detected to produce the image currents. The frequency of the second local source may be 5120 kilocycles, giving an intermediate frequency of 120 kilocycles.

The invention itself may be more readily understood. by reference to the following detailed description in connection with the drawings, in which:

Fig; l shows diagrammatically a radio television transmitting station; and

Fig. 2 shows diagrammatically a radio television receiving station.

Referring to Fig. l, there is shown a face l() which represents the imagev to be transmitted positioned in front of the scanning apparatus. Light'from a lamp l1 is focused into a pencil or beam of rays by the optical systemv l2 and directed against the surface ipo lu kn a srainiinpY difzc lil which is provided near rinz with a plur: li 1y of spirally arranged rationa rl"hcre is provided in trontof the scanning dis a shield 14 having an openc .eh width that the scanning dise re oh ce the iight comingthrough one pez'- toratien at a time .vill pass thereaeross in )roiimatelrihoriijontal line. 'm

rae light through the opening in the shieldwll-lf` le feeusedby means ot aliens 15 upon the tace l and ia reflectedy therefrom upon the sensitive surface of a pho-toelectrie cell which rates an electrical Wave ot characteristics depending' upon the light and shade va riations in the reflected beam. This scf vand the reproducing' canning' v ein out ined hereinafter are described in nere de ail in the copending` application ot' ffl' 'aj Serial No. 181,538 filed April (j. 1927. The scanning dise 13 d iven by a motor 17 which is driven at such a speed as to anse the light pencils through the disc to completely scan the image about 18 times per second. Synchronizing appz ratas 18 is im vided 'tor holding the motor and scanningr disc in synchronism with the scamling disc at the receiving' station, the synchronizing; currents being transmitted over a radio channel and being' received in the radio receiver lf). Obviously the synchro'iization ot' the scanning discs may be controlled from the transmitting` station it' preferred.

The electrical. waves produced by the pho to-electrie cell 16 have components of trequency ranging' from about 10 to 20,000 cycles per second. These Wives are amplified in electric discharge amplifiers 20 and 2l. and en'iployed Ytor nimlulatingr a radio-trequem'y ra ve in the radio transmitting circuit. The radio transmitter comprises a source of radio ti 4fuiency waves which may be an elec- Lv ric discharge oscillator, for example of the typ-e described in Hartley Patent 1,350,763 o October 2(iv 1920.y for generating a Wave 1,575 li. c. per second. The output of source is ainplilied in an electric disc iai-ge amplifier 23 and impressed upon the input ot an au plifyingpinodulator 211 ot the constant current type described in l-l'eisinrg Pat-ent 1,442,147 of January 10, 1923. The output ot the image Wave poW-r amphiier 21 is impressed upon the anode circuit of the amplifyingv Vmodulator 24, to modulate the radio-frequency Waves in the manner described in the Heising' patent. The resulting' modulated radio ave is amplified in an electric discharge power amplilier 25 and impressed through the capacity coupling' circuit 2G upon a t 'ansmission line 27 which connects the transmitter and the antenna. The other terminal ol the line 27 is connected through a second capacity coupling circuit 28 and a radio trequency transformer 29 to the radiatinp' antenna 30.v y

u spite ot the tact that the radio equipment Separated from the antenna, beine' connected thereto by the line 27, much diiliculi): is caused by the radio frequency lields produced in the neighborhood of the radio equipment due to the relatively high amplifica-'tion )which muet be employed with photoelectric cells. in order to minimize trouble of this nature the television tern'inial appa- !s propo' is located Within a speciallyv shielded studio. oi the studio are completi covered with Yo. gauge sheet copper lapp d about one inch and carefully soldifred. rEhe .vindon's are coi/'cred with i'ine copper gauze. The door is covered with ali/ect copper which is carried around the edges ao that in closingy it maires: a firm wiping' Contact W'th the surrounding ll'alne. Circuits lor lighting' and miscellaiieous poiver are led in through specially roustructed transtormrns litted with groundei copper sbielda between the primary and sercndary Windinps rthe circuits leadingr vtroni the television transmittingil appar: tua to the radio transmitter are run in lead cablea and brought into the room through suitable radio frequency filters enclosed in cable boxes attached to the copper sheathing. In order to a' ,d the possibility ot the heavy current leads to the arc bri ing,r in radio trequcin-y energy and to einnnate noise and heat from the are; it is mounted in a metal cabinet located outside oi' the room'. This tabinet is grounded to the sheathing so as to protect the circular openingV through which the light beam is projected into the room.

.lin the receiving' station shown in Fie'. 2.y thmodulated radio rave is received in a detuned antenna 4t'. selected b v tivo capacity coupled tuned circuits f l and 32 and imnressed upon a modulator circuit M1 to modulate toe output o'l1 a 6.575 k. c. oscillator O1. 'Vlie resulting sideband centering about 5.000 lr. c. is si lected in the capacity coupled tuned circuits 33 and 3% and impressed upon thc modulator M2 to modulate the output ot a 5,120 li. c. orcillator OL, and produce an intermcdiate-trequcncf,v sirlel-ani'l centering about 120 k. c. This intermediate l'ircqucnovY fave is selectively anipliiied in the intermediate frequencj.v amplitiers UTAX and IFA: and detected in the detector circuit D, the resulting image waves leien' a'mpiil'ied in the low-trequencv amplifier AFA and impressed upon the television reproducing apparatus.

This reprodluingr apparatus comprises electric discha amplifier 35 the output olE which is connected to a neon glow lamp 30 Which is placed en one side ot a scaunin;` disc 37 similar to the sianning disremplojyed at the tra 'nf-m ittine' Station. The operator view#` the reproduced image through a shield 38 having` an opening of such size as to permit one aperture of the dise 37 to be viewed therein at a time. The disc 37 driven hy a constant speed motor 56 which also drives a syn- (lll The wails. ceiling; and lioor Lesen-r vrhronizing apparatus 39 the output of which is employed for modulating a radio frequency wave in the radio transmitter 40 which transmitted to the transmitting station to synchronously drive the transmitting scanning disc as herei'nbefore described.

The oscillators O1 and O2 are of the type described in Hartley Patent 1,356,763 of'October 26, 1920. Oscillator O1 comprises a three-electrode discharge device 41 associated with a frequency determining circuit 42 inductively coupled to which is an inductance coil 43 which is connected to the grid of the three-electrode discharge device 44 employed in the modulator circuit M1. Similarly, the oscillator circuit O2 comprises a three-electrode electric discharge device 51, a frequency determining circuit 52 and an inductance coil v53 coupled therewith and connected to the grid of the three-electrode electric: discharge device 54 employed in the modulator circuit M2. The plate circuit of the device 54 is connected to the grid circuit of a three-electrode discharge device 57 through a filter 58 which, as is Well understood in the art, may be de signed to transmit the intermediate frequency side bands and to suppress Waves of other frequencies. The plate circuit of the device 5T is connected to the grid circuit of another three-electrode electric discharge device v employed in vthe second intermediate frequency amplifier circuit through an inter stage transformer 60. The plate circuit of the device 59 is connected to the grid circuit of a three-electrode `electric discharge detector 61 through a second filter 62 similar to filter 58. This filter is designed to have a low input impedance at 120 lz. c. to improve the action of detector circuit. The plate circuit of the detector 61 is connected to the grid circuit of a three-electrode electric discharge device 63 through a low pass filter G4 and the plate circuit ofthe amplifying device 63 is coupled to the input of the amplifier 35 through a transformer 65.

The electric discharge devices 41, 44, 51, 54, 57, 59, 61 and 63 are supplied With cathode heating current from a battery G6. With space current from a battery 67, and With grid biasing potential from a battery 68 with Which there is'associated a potentiometer 69 so as to provide the proper potentials. Condensers and resistances are employed in a manner well understood in the art for confining the direct and alternating currents to their respecti ve paths.

The capacity coupled tuned circuits 31 and 32 serve toselect the received radio Waves to the approximate exclusion of interfering waves. However, it is difficult to provide for any high degree of selectivity by such arrangements since they must be designed to pass a 2.6% band, the radio sidebands being 3 about 40,000 cycles in Width. In accordance with the invention, the selected band is beat up to Aabout 5,000 k. c. by the use of the oscillator O1 and modulator M1. At this frequency the desired sidebands require only a 0.8% band which can be readily obtained With a high degree of selectivity by the use of the capacity coupled tuned circuits 33 and 34. Vfhus itV is possible to sharply discriminate against interfering ivaves without distortiupthe required Wide band.

In order to obtain sufficient amplification the selected band is beat down to about 120 lr. c. and selectively amplified in the intermediate frequency amplifiers IFAL and llTAQA after which the Waves can be detected and the resulting image Waves amplified by means of the usual lovv frequency amplifier circuits V/That is claimed is: 1. In a system for producing images of moving objects, means for producing image formi ng waves of a band of frequencies of the order of 20.000 cycles in Width, means for generating a radio carrier Wave of frequency of the order of 1,000 kilocycles or more, means I for modulating said carrier Wave in accordance with said image forming waves, means for radiating said modulated Wave, means for selectively receiving said modulated Wave, means for combining the received Wave with another Wave to produce asecond modulatet Wave of the order of 5,000 kilocycles, means for selectively transmitting said second modulated Wave to the substantial excluon of interfering Waves, means for combinp iiig said second modulated Wave with another ivave to produce a third modulate-d Wave of the order of 120 lrilocycles, means for selectively amplifying said last mentioned Wave, means for detecting said selectively amplified Wave to produce the original image Waves, and means for producing an image from said repro-duced band of Waves.

2. In a system for producing images of moving objects, means for producing image forming vvaves of a Wide range of frequencies, means for generating `a radio carrier Wave of frequency of the order of 1,000 kilocycles or more, means for modulating said carrier wave in accordance with said image forming Waves, means for radiating said modulated Wave. means for selectively receivin .frsaid modulated Wave. means for gen eratin g a Wave of frequency higher than said modulated ivaif'e. means for combining said Wave with said modulated Wave to produce a difference component of frequency higher than vthat of said modulated Wave, means for selecting said difference component to the substantial exclusion of interfering Wave" means for generating another Wave, means 1 .r comlbining said last mentioned Wave with said selected component to produce a second difference component of frequency lower than that of said first modulated Wave, means for selectively amplifying said last mentionedt ibo component Wave, means for detecting said amplified component Wave to reproduce the original image n' ves, and means for producing an image in response to said reproduced waves.

3. In a system for producing images of moving objects, means for producing image forming Waves of a n'ice range of frequencies, means for generating' a radio carrier Wave of frequency of the oi'der of 1,000 liilocycles oi' more, means for modulating said carrie-i' 'ware in accordance 'with said image forming Wares, means for radiating said mod lated Wave, means for selectively receiving said niodniaited nare, means for geaerating a Ware of frequency higher than said modulated Wave, means for combining said Ware with said modulated rifare to produce a dii'i'erencc ceiiiponent of frequency higher than that of said modulate-:l nave, fiieans for selecting said dii'iference compoin 't to the substantial exciusion of interfering wave?, means for amplifying and deniozlulatinf" i selected ware to regi-mince the innig"- ing' Ware, and means for prodi; in response to said reproi'lnced era i. ln a system for prod .cing imag-s of moving objects, means for prediking image forming Waves of :i Wide rai f frequencies, ineens for generating :i radio carrier for modulating said carrier Wave, means Wave in accor in-ce wiri said i'ziiagi-i foriimag" Waves, means for radiating and selectively receiving' sain modulated wave with negligibie r istortion of the iniae'e side band, means for generating a wave of frequency higher than said modulated wave. means for ccmbining said Ware with said ii'iod'iilated Wave to produce a dil/ference component of frequency higher than that of id modulated Wave, means for selecting said dii'ierence component to the subsv ltial e. ion of iii-- terfering Waves, means for np tying and demodnlating said selected ware to reproduce 'the image forming Ware, and means for producing an image in response to said reproduced Wave.

5. In a system for producing' images of moving objects, means for producing image forming Waves of a iride rang/:e of frequencies, means for generating a radio carrier Ware, means for modulating' said carrier Wave in accordance With said image forming` wares. means for radiating and seiectiielr receiving` said modulated Wave with negligible distortion of the image side band, means for conihining the received Wave with another Wave to produce a, second mofliilateigl Wave of the order of 5.000 lrilocycles, means for selectively transmitting' said second modulated Wave t the substantial e? :lesion of interfering Waves, means for combining said second modulated Wave with another Wave to produce a third modulated War-e of the order of 120 kilocycles, means for selectively i Iii amplifying said last mentioned Wave, means for detecting said selectively amplified Wave to reproduce the original image. waves, and means for producing an image from said reproduced band of Waves.

6. In a system for producing images of moving objects, means for producing` image forming Waves of a Wide range of frequencies, ine-ans for generating a radio carrier wave, means for modulating said carrier wave in accordance with said image forming waves, means for radiating and selectivelyy receiving said modulated Wave with negligible distortion of the image sidehand, means for generating a wave of frequency higher than said modulated wave7 means for combining said Wave With said modulated ware to produce a difference component of frequency higher than that of said modud wave, means for selecting said differcnce component to the substantial exclusion of interfering Waves, means for generating .another Ware, i cans for combining said last mentioned Wave With said selected component to prodiice a second difference component of frequency lower than that of said first modul ated Wave, means for selectively amplifying' said last mentioned component were, means for detecting said amplified minnonent wave to reproduce the original ini'r re n'aif'es, and means for producing an in i, in response to said reproduced wares.

EDWVARD L. NELSON. 

